Electric signal amplifier



March 15, 1932. w L. CARLSQN ELECTRIC SIGNAL AMPLIFIER Filed April 10,1950 Inventor: Wendell L. Carlson by His -Atto r*neg.

Patented Mar. 15, 1932 V UNITED STATES PATENT QFFICE WENDELL L. CARLSON,OF .I-IADDO'NFIELD', NEW JERSEYQASSIGNOR TO GENERAL ELEC- TRIC COMPANY,A CORPORATION OF NEW YORK ELECTRIC SIGNAL AMPLIFIER Application filedApril 10,

The present invention relates to electric signal amplifiers embodyingelectric discharge amplifier devices, and more particularly it relatesto means for controlling the signal volume secured from the output ofsuch amplifiers. I

It is the object of the present invention to provide an improved meansfor controlling the signal volume secured from the output of anelectricdischarge amplifier apparatus which operates in such a manner thatnoises which may be introduced into the output by the electric dischargedevices are reduced to amimmum. V 0 The invention will be betterunderstood from the following description when taken in connection withthe accompanying drawing and its scope will be pointed out in theappended claims.

' In the drawing, the figure is a schematic wiring diagram of anelectric signal amplifier embodying electric discharge amplifier devicesand provided with means embodying the invention, for controlling thesignal volume secured from the output of said amplifier.

Referring to the drawing, 5 and 6 are electric discharge devices of thefour-element vacuum tube type, cascade connected in an electric signalamplifier between an input circuit 7 represented by the primary of aninput transformer 8 and an output circuit 9 represented by the secondaryof an output transformer 10. An intermediate transformer 11 serves tocouple the devices 5 and 6 together in cascade.

Suitable operating potentials forthe anode and grid bias circuits of theelectric discharge devices or tubes are supplied through leads 12 and asupply resistor 18, 14, from which resistor suitable operating anodepotentials are taken in the usual manner, as indicated in the drawing. a

Connected with at least one of said electric discharge devices is ameans for controlling the transmission efiiciency of said device. Suchmeans may be arranged to control the operating potential upon any one ofthe various elements of the electric discharge device, as is well known.In the present example, con- 1930. Serial No. 443,196

the fixed resistor 15 provides a fixed amount of bias for the electricdischarge devices or amplifier tubes while variable resistor 18 providesan additional variable bias in series with the fixed bias provided byresistor 15; The resistor shown in the present example is varied bymoving. the contact arm'20 along the resistor and between the terminals19. As shown in the drawing, movement of the contact to the left servesto increase the resistance in circuit with fixed resistor 15 and toincrease the amount of bias applied to the electric discharge devices 5and '6. As the bias voltage on the grids 17 is increased, it will beunderstood that the amplification or transmission efliciency of theelectric discharge devices is reduced. Thus, by moving the contact arm20 to the left, as viewed in the drawing, the signal volume delivered bythe arm plifier to the output circuit 9 is gradually reduced. I When theamplifier devices 5 and 6 are operating at maximum efficiency for thetransmission of the signals through the amplifier, such operation may beaccompanied by a hiss or undesirable sounds of operation introduced intothe output because of the sensitive condition oi? operation of theamplifier devices. It is, therefore, desirable to operate such devicesslightly below their maximum operating efliciency. In' the presentexample, this is done by slightly increasing the negative bias appliedto the grids 17, thereby reducing the sensitivity of said devicesthrough the medium of thecontrol means 18. It will be noted that thefixed'resistor 15 and the variable resistor 18 are suitably bypassed bya fixed capacity 21 connected'with may be insufiicient for the propercontrol of the signal volume delivered by the amplifier.

For example, in the presence of strong signals from an antenna andground system 2223, when applied to the input circuit 7 directly,overloading of the input amplifier device or tube 5 is almost certain toresult.

Accordingly, there is provided in connection with the input circuit 7 ameans for varying the signal strength applied to said input circuit. Inthe present example this isin'a form of a variable resistor 24:introduced between a pair of signal supply tor minals 25 and 26 and theinput circuit 7, said terminals being connected respectively with theantenna 22 and the ground 23.

' The resistor24 is provided with a movable element or contact 27 whichis movable'between terminals 25' and 26 and along the resistor 24. Themovable contact 27 is connected withthe input circuit 7 while theopposite 'sideof the input circuitis connected'with the grounded inputterminal 26. V

The, variable resistor 24' is providedwith an-inactive resistanceportion 28, over which movement of contact 27 produces no appreciablechange in the resistance between either of the terminals 25 and 26 andthe contact arm 27. The arrangement is such that the movable control armor contact 27 may be moved an appreciable distance through its range ofmovement represented by the terminal limits 25 and 26 without efiectingany appreciable. control of the input signal volume applied to'the inputcircuit 7. As the movable member 27 is further moved toward the groundor low potential terminals 26, re-

.sistance is gradually introduced into the antenna circuit and alowerand lower resistance is placed in shunt with the input circuit 7 therebyserving to reduce the signal strength applied to the input circuit 7.Any other suitable arrangement of a control means for varying the signalvolume or signal strength applied to the input circuit may be employed,however, providing that it is also arranged to efl'ect no appreciablechange in the input signal strength over a portion of its range ofmovement.

-With the means for controlling the signal volume at the input soarranged, it is connected with the movable member 20 of control means 18and a common control means indicated'at29 through any suitable meanssuch as a common shaft 30, thus providing a dual volume or signal outputcontrol for the amplifier.

With this arrangement, it will be seen that when reducing thetransmission eificiency oi the amplifier devices, thereby to reduce thevolume or the signal output, during the first portion of the movement ofthe control means the movable element 20 of the bias control meansserves to increase the resistance in the cathode circuit which increasesthe negative bias on the tubes 5 and 6, while movement of the member 27of the controlmeans 26 does not appreciably effect the signal strengthapplied to the input circuit 7.

lVith the transmission efficiency or sensitivity of the electricdischarge amplifier thus partially reduced, the signal output is furtherreduced by continuing to reduce the sensitivity or transmissionefficiency of the amplifier devices while the input energy or signalvoltage applied to the, input circuit of the amplifier is also reducedsimultaneously. Likewise, when the output volume is increased, thesensitivity or transmission efiiciency-of the amplifier issimultaneously increased along with the input energy or signal voltageapplied to the input circuit, until the maximum signal strength isapplied to the input circuit while the sensitivity or transmissionefficiency I re ofthe amplifier is at a reduced value. For

increased signal output, the sensitivity or transmission efficiency ofthe amplifier 1S further increased up to a desired maxlmum pointdetermined by the limit of the selected range ofcontrol of thetransmission efiiciency of the particular electric discharge device ordevices employed. r

This arrangement of controls has been found to be very eflective, inproviding for quieter operation of a signal amplifier embodying electricdischarge devices. The dc layed control feature in connection with themeans controlling the input signal strength may be applied to anyelectrical signal amplifier having aninput circuit and means forcontrolling the transmission eificiency of at least one of the electricdischarge amplifier devices. It is particularly well adaptedfor thecontrol of electric signal amplifiers em ployed in connection with radioreceiving apparatus and the like.

What I claim as new and desireto secure by Letters Patent of the UnitedStates, is :v

1. -The combination with an electrical signal amplifier having an inputcircuit, an output circuit and at least one electric discharge amplifierdevice connected between said circuits for the transmission of signalsfrom said input to said output circuit, of means for varying thetransmission efiiciency of said amplifier device between predeterminedlimits, and means forvarying thesignal strength nal amplifier having aninput circuit, an output circuit and at least one electric dischargeamplifier device connected between said circuits for the transmission ofsignals from said input circuit to said output circuit, of meansprovided with an element movable between certain limits to vary thetransmission efiiciency of said amplifier device, means for varying thesignal strength applied to said input circuit, said last-named meansbeing operative to reduce the signal strength applied to the inputcircuit only after the transmission eiliciency of the amplifier deviceis partially reduced by said first-named means, and means for operatingsaid second-named means simultaneously with said first-named means.

3. The combination with an electrical signal amplifier having an inputcircuit, an output circuit and at least one electric discharge amplifierdevice connected between said cir cuits for the transmission of signalsfrom said input to said output circuit, of means provided with anelement movable between certain limits to vary the transmissionefliciency of said amplifier device, a variable resistor,

said resistor having a movable element arranged to vary the signalstrength applied to said input circuit, the movement of said elementbeing efiective to vary the signal strength only over a portion of itsrange of movement, and means connected with said movable elements formoving the same simultaneously.

4:. The combination with an electrical signal amplifier having signalsupply terminals, an input circuit, an output circuit and at least oneelectric discharge amplifier device connected between said circuits forthe transmission of signals from said input to said output circuits, ofmeans provided with an element movable between certain limits to varythe transmission efi'iciency of said amplifier device, means for varyingthe signal strength applied to said input circuit from said supplyterminals, said last-named means including a variable resistor connectedbetween said supply terminals and said input circuit and having amovable control element by which said signal strength is varied, the

vmovement of said control element being efiective to vary the signalstrength over a portion only of its range of movement, and a cuit, saidmovable elements having the same range of movement and the elementmovable to control the signal strength having a lesser range ofefiective control.

6. The combination with an electrical signal amplifier having an inputcircuit, an output circuit and at least one electric discharge amplifierdevice connected between said circuits for the transmission of signalsfrom said input to said output circuits, of means simultaneously movableto vary the transmission efficiency of said amplifier device and asignal voltage applied to said input circuit, the range of movement ofthe transmission eificiency varying means exceeding the range of controlof the signal voltage varying means in a direction of movement toincrease the transmission efi'iciency. I

7. The combination with an electric signal amplifier having an inputcircuit, an output circuit and at least one electric discharge amplifierdevice connected between said circuits for the transmission of signalsfrom said input circuit to said output circuit, of means provided withan element movable between certain limits to vary the transmissionefficiency of said amplifier device, and means for varying the signalstrength applied tosaid input circuit, said last-named means beingoperative to reduce the signal strength applied to the input circuitonly after the transmission efliciency of the amplifier device ispartially reduced by said first-named means. I

In witness whereof, I have hereunto set my hand this 7th day of April,1930.

' WENDELL L. GARLSON.

common means for moving said elements simultaneously.

5. The combination with an electrical signal amplifier having an inputcircuit, an output circuit and at least one electric discharge amplifierdevice connected between said circuits for the transmission of signalsfrom said input to said output circuits, of means having a commoncontrol and provided with movable elements 'for varying the transmissionefficiency of said amplifier device and the strength of signals receivedby said input cir-

